In the case of LED driver designs that linearly regulate the LED current and hence the mains current and whose power draw means that it is necessary to ensure a largely sinusoidal current draw from the mains, a resistor divider connected to the rectified AC supply voltage has to date been used to derive a setpoint value for the current regulator. Since this input voltage is sinusoidal, this means that also the setpoint value and, in the case of suitable control design, also the actual value of the mains current are sinusoidal.
However, this arrangement encounters the problem that fluctuations in the mains voltage entail fluctuations in the current, which firstly significantly increases the losses in the linear current regulator in the event of overvoltage and secondly results in an excessively low LED current in the event of undervoltage.
Solutions to date have taken action in the setpoint value formation for the LED current by stipulating a maximum value that never exceeds this setpoint value, for example. However, in the event of overvoltage, this results in the mains current draw no longer being sinusoidal.
Another known option involves the use of a multiplier to produce a setpoint value. In this case, the multiplier multiplies a sinusoidal voltage obtained by means of the aforementioned voltage divider by a value that is constant at least within a few mains half-cycles, and, at its output, provides a sinusoidal voltage having an amplitude that is variable in comparison with the mains voltage. A drawback in this case is the relatively high level of circuit complexity for the multiplier.